This is continuing investigation into the relationship between physiological cerebral processes and conscious or subjective experience. The specific aims are to extend this to the issue of perception without awareness, by establishing whether stimuli in the specific projection pathway of the somatosensory system (e.g., VPL nucleus in thalamus) can be detected by the human subject even when they are inadequate to elicit any conscious sensory awareness. We want to examine the time factor of stimulus duration (i.e., train duration of the repetitive pulses) in distinguishing inputs that are adequate for awareness from those that can be detected without awareness, with stimulus intensities (peak currents) well above the minimum needed to elicit cortical neuronal responses (evoked potentials) with each pulse. The study will be a partial test of our general hypothesis that brief cortical activations of suitable amplitudes or magnitudes may subserve unconscious psychological or mental functions, but that the activations must endure for some substantial time (up to about 500 msec, depending on intensity) in order also to elicit a conscious experience. An increased understanding of the cerebral physiology of conscious and unconscious functions is fundamental to psychiatric and psychological theories in this area.